1. Field of the Invention
The present invention relates to a two-step electric switch which actuates two switching circuits sequentially, by two-step depressing operation. More particularly, the present invention relates to the two-step electric switch which can be used for printed circuit board effectively because of improved switch contact springs.
2. Description of the Related Art
There are several disclosures regarding this type of two-step switch, for example, patent documents 1 and 2, as follows:
Patent Document 1: Official Gazette of Japanese Unexamined Patent Publication No. 2002-352664; and
Patent Document 2: Official Gazette of Japanese Unexamined Patent Publication No. 2002-163952.
FIG. 18 shows a structure of a two-step switch according to the Patent Document 1. FIG. 18 is a perspective view of a switch contact spring 201, having a center disk 203, a ring frame 205 positioned along the outer periphery center ring 203, connecting chips 207, 207 connecting the center disk 203 to the ring frame 205, and supporting chips 209, 209 provided on the outer periphery of the ring frame 205.
There is a first movable contact on the outer periphery of the lower surface of the center disk 203. There is also a second movable contact on the lower surface of the center of the center disk 203. A regular contact is provided on the lower surface of the ring frame 205. On the other hand, there is an insulation housing (not shown) under the switch contact spring 201, on which a common contact, a first selective contact and a second selective contact are provided in this order from the outer periphery of the switch contact spring 201.
According to the above structure, the regular contact of the switch contact spring 201 is regularly in contact with the common contact. When a first click operation is done, the first movable contact of the switch contact spring 201 becomes in contact with the first selective contact, whereby a first electric circuit is provided. Then, when a second click operation is done, the second movable contact of the switch contact spring 201 becomes in contact with the second selective contact, whereby a second electric circuit is provided.
However, the conventional two-step switch according to the above disclosure has several disadvantageous points.
First, as illustrated in FIG. 18, the switch contact spring 201 according to the prior art has a dual structure in radial direction, i.e. the structure in which the ring frame 205 is positioned along the outer periphery of the center disk 203. Consequently, the size of switch would become larger in radial direction, and it is impossible to provide a small-size two-step switch.
For reference, as long as the present invention concerns, “small-size” means, for example, various two-step switches incorporated in narrow spaces, such as for portable telephones, etc.
Second, according to the two-step switch of the prior art, for the purpose of securing the (depressing) stroke, different levels should be provided on the fixed contacts in perpendicular direction. In particular, the different levels are provided among the common contact, the first selective contact and the second selective contact of the insulation housing, so that the necessary stroke may be secured. However, it is very difficult to provide such different levels on a printed circuit board, hence, the switch contact spring 201 according to the prior art cannot be used by simply making in contact with the printed circuit board.
Third, when the conventional switch is used for the printed circuit board, the switch contact spring 201 must be soldered, thus the switch should be made of any durable material against high temperature, which would increase the production cost.
Fourth, according to the switch contact spring 201 as shown in FIG. 18, two different loading characteristics must be provided by the single contact spring, which would require difficult adjustment working, having poor flexibility to be applied to various specifications.